Heating, ventilation, and air conditioning (HVAC) systems consume a large amount of energy. Commonly, heating and cooling operations for an environment are controlled automatically with one or more thermostats. A thermostat can be located centrally, or thermostats can be distributed. Typically, the operation of the HVAC system is according to preset temperature limits.
Because many environments may be unoccupied at times, this wastes energy. Occupancy can be determined with motion detectors. However, the time required to heat or cool the environment to the desirable temperature takes considerable time, perhaps longer than the time that the environment is occupied.
An operation schedule can be used. However, this is impractical when the occupancy period is irregular, or the schedule changes frequently. Schedules also do not accommodate holidays, vacations, travel, unplanned absence, and other changes to the occupancy routine. Thus, the schedule is only a best guess of occupancy.
One system augments manual and programmable home thermostats by using just-in-time heating and cooling based on travel-to-home distance obtained from location-aware mobile phones, Gupta et al., “Adding GPS-Control to Traditional Thermostats: An Exploration of Potential Energy Savings and Design Challenges,” Book Pervasive Computing, Volume 5538/2009, pp. 95-114 May 2009. The system starts heating or cooling an inhabitable space only when the time necessary for the space's occupant to reach that space becomes lower than the time it would take to bring the space to a comfortable temperature.
That system used a GPS-enabled device such as a telephone to determine a user's current location, and a publicly available mapping system (MapQuest®) to compute the time to reach the space to be conditioned from the user's current location.
In order to compute the time necessary to bring the space to a comfortable temperature, that system uses empirical data stored in heating/cooling look-up tables. For a given combination of indoor and outdoor temperature, the table stores the time it would take to heat or cool the space to a comfortable temperature. Each table is specific to the heating/cooling system type installed at the particular location. That system lacks generalization, because the tables must be individually constructed for each residence from measurements. Furthermore, the observed data from a limited time period typically would not include all possible combinations of indoor and outdoor temperatures that might be encountered in the future.
Another disadvantage of that system is the need to constantly re-compute and compare the travel time and conditioning time. Since the GPS-enabled mobile device is typically powered by a battery, constant communication between the device and the conditioned space would quickly drain the mobile device's battery, and is also likely to result in costly data communications traffic.